1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine which controls a fuel quantity to be supplied to the engine and the timing of the ignition. More particularly, it relates to how to control an engine at the time of adjusting ignition timing.
2. Discussion of Background
FIG. 12 is a block diagram showing a construction of a conventional control apparatus for an engine. In FIG. 12, a reference numeral 1 designates a reference angle sensor which outputs a reference angle signal SG by detecting a predetermined angle before the top dead center point of the crank angle, e g. an angle of BTDC 75.degree., of the engine, a numeral 2 designates an intake air pipe pressure sensor to detect a pressure in an intake air pipe in the engine, a numeral 3 designates an ignition timing adjustment signal generator which is constituted by, for instance, a switch whose one terminal is grounded and which is so operated that it is turned on at the time of adjusting the timing of ignition so that a ground potential signal is generated, a numeral 4 designates an idle switch which is turned on when it detects an idling position of a throttle valve in the intake air pipe of the engine, a numeral 5 designates an O.sub.2 sensor which detects a concentration of oxygen in the exhaust gas, a numeral 6 designates a base advance angle value operating means which calculates a base advance angle value of ignition timing on the basis of an engine revolution number and an intake air pipe pressure, a numeral 7 designates a correction means for stabilizing idling which corrects the base advance angle value so as to eliminate the difference between an actual revolution number and an average revolution number at the time of idling operations, a numeral 8 designates a target advance angle value changing means which selects either a fixed advance angle value or a target advance angle value from the correction means for stabilizing idling 7 in accordance with a signal from the ignition timing adjustment signal generator 3 and generates an output in accordance with the selection, a numeral 9 designates an advance angle time converting means which converts the selected target advance angle value into a time, a numeral 10 designates an ignition signal output means which outputs an ignition signal IGT immediately after a period of time converted by the converting means 9 has passed, on the basis of the reference angle signal SG, a numeral 11 designates an ignition device comprising an igniter, an ignition coil, a distributor, an ignition plug and so on, which effects ON/OFF control of a primary current of the ignition coil in response to the ignition signal IGT applied thereto, a numeral 12 designates a base fuel quantity operating means which operates a base fuel quantity on the basis of an engine revolution number and an intake air pipe pressure, a numeral 13 designates a feed-back correction means which corrects the calculated base fuel quantity upon the receipt of an output from the O.sub.2 sensor 5, a numeral 15 designates a fuel injection signal output means which converts a fuel quantity into a time for driving a fuel injection valve so that a fuel injection valve 16 is actuated in synchronism with the reference angle signal SG during the time determined by the fuel injection signal output means, and a numeral 17A designates an electronic control unit which is constituted by the above-mentioned structural elements 6-10, 12, 13 and 15 and which generates the above-mentioned ignition signal IGT, fuel injection signal and so on.
The operation of the conventional control apparatus will be described.
The reference angle sensor 1 for detecting a crank angle position of the engine outputs a reference angle signal SG which rises at a crank angle of BDTC 75.degree. and falls at a crank angle of BTDC 5.degree..
The base fuel quantity operating means 12 calculates a base fuel quantity by mapping a two-dimensional map which is prepared on the basis of an actual revolution number signal Ne which represents an actual revolution number of the engine which is obtained based on the reference angle signal SG, and a pressure signal Pb which represents an inner pressure of the intake air pipe which is detected by the intake air pipe pressure sensor 2.
The output V.sub.02 of the O.sub.2 sensor 5 is such as shown in FIG. 5, namely, when the air fuel ratio exceeds a value of 14.7, the output is at a lean value which is less than a threshold voltage V.sub.th, and when the air-fuel ratio is less than 14.7, the output is at a rich value which exceeds V.sub.th.
The feed-back correction means 13 receives the output voltage V.sub.02 of the O.sub.2 sensor 5 and treats the output voltage V.sub.02 with proportion and integration processes to thereby obtain a feed-back correction coefficient K.sub.FB (FIG. 6). Then, the correction means 13 outputs a signal indicating a fuel quantity by multiplying the base fuel quantity obtained by the base fuel quantity operating means 12 by the coefficient K.sub.FB.
The fuel injection signal output means 15 converts the fuel quantity into a time for driving a fuel injection valve and outputs a fuel injection signal having a time width corresponding to the time for driving the fuel injection valve in synchronism with the rising of the reference angle signal SG, so that the fuel injection valve 16 is actuated. Thus, fuel is injected into the engine through the fuel injection valve 16.
On the other hand, the base advance angle value operating means 6 calculates a base advance angle value by mapping a two-dimensional map which is obtained based on an actual revolution number signal Ne which is obtained on the basis of the reference angle signal SG and a pressure signal Pb. The correction means for stabilizing idling 7 outputs the base advance angle value as a target advance angle value without any correction when the idle switch 4 is in an OFF state at the time of non-idling. The correction means for stabilizing idling 7, when the idle switch 4 is in an ON state at the time of idling, outputs the target advance angle value by correcting the base advance angle value in response to a value of difference between an average revolution number signal Na obtained on the basis of the reference angle signal SG and the actual revolution number signal Ne. The characteristic of the correction means for stabilizing idling 7 is shown in FIG. 7. Namely, when the actual revolution number is less than the average revolution number, a correction angle for stabilizing idling .DELTA..theta. is shifted to a positive (+) value, i.e., by correcting the base advance angle value to the advance angle side in an amount corresponding to .DELTA..theta. to thereby increase the actual revolution number. On the other hand, when the actual revolution number is more than the average revolution number, the base advance value is corrected toward a delayed angle value in an amount corresponding to .DELTA..theta. by shifting .DELTA..theta. to the negative (-) side, whereby the actual revolution number is reduced.
The target advance angle value changing means 8 selects a fixed advance value as a target advance value when it receives a ground potential signal from the ignition timing adjustment signal generator 3 and outputs a signal corresponding to the target advance angle value. On the other hand, the target advance angle value changing means 8 selects an advance angle value which is provided from the correction means for stabilizing idling 7 as the target advance angle value when it does not receive the ground potential signal, and outputs a signal corresponding thereto.
The advance angle value-time converting means 9 obtains a period T.sub.1 corresponding to a crank angle of 180.degree. from the reference angle signal SG, and converts the target advance angle value .theta..sub.ADV selected by the target advance angle value changing means 8 into a time T.sub.a.
The ignition signal output means 10 receives a signal indicating the time T.sub.a and changes the output having an H level to an output having an L level when the time T.sub.a has passed from the rising of the reference angle signal SG, outputting the ignition signal IGT of L level to the ignition device 11. Thus, the ignition device 11 fires a gas mixture in the combustion chamber of the engine.
The reference angle signal SG and the ignition signal IGT are generated at the timings shown in FIG. 8. Namely, when the target advance angle value .theta..sub.ADV is expressed by an angle of BTDC, the target advance angle value .theta..sub.ADV can be converted into T.sub.a by using the equation ##EQU1##
In the conventional control apparatus for an engine having the construction as described above, when the ignition timing adjustment signal generator 3 generates a ground potential signal, namely, when the generator 3 is turned on, a fixed advance angle value is selected. In the case where the engine is idling, correction for stabilizing idling becomes null, whereby control by a change of revolution number is lost.
Since the feed-back control of the air-fuel ratio is conducted at the above-mentioned time, the air-fuel ratio can be converged to a point near a stoichiometric air-fuel ratio, but fluctuation in revolution number becomes large. Generally, when a timing light is irradiated to the crank shaft at the time of adjusting ignition timing, the scale of the crank shaft apparently stops, which enables the adjustment of the position of the reference angle sensor 1. However, when the fluctuation of the revolution number takes place at that moment, the scale of the crank shaft does not apparently stop, but it turns. Further, in a case of using a period estimation type ignition timing control system, it is difficult to estimate the period, and the timing of the ignition fluctuates, whereby it is difficult to adjust the ignition timing.
Further, there has been known a control apparatus for an engine as shown in FIG. 13. The conventional apparatus is the same as the apparatus as shown in FIG. 12 except that the later excludes the O.sub.2 sensor 5 and the feed-back correction means 13. Accordingly, the same reference numerals designate the same or corresponding parts and description of these parts is omitted.
The operation of the conventional apparatus shown in FIG. 13 will be described.
The reference angle sensor 1 which detects the crank angle position of the engine generates a reference angle signal SG which rises at a crank angle of BTDC 75.degree. and falls at a crank angle of BTDC 5.degree.. The base fuel quantity operating means 12 calculates a base fuel quantity by mapping a two-dimensional map on the basis of an actual revolution number signal Ne representing an actual revolution number of the engine which is obtained on the basis of the reference angle signal SG, and a pressure signal Pb which represents an inner pressure of the intake air pipe which is detected by the intake air pipe pressure sensor 2. The fuel injection signal output means 15 converts the base fuel quantity into a time for driving a fuel injection valve and outputs a fuel injection signal having a time width for driving the injection valve in synchronism with the rising of the reference angle signal SG, by which the fuel injection valve 16 is actuated. Thus, the engine is supplied with fuel by the fuel injection valve 16.
The operations concerning the reference advance angle value operating means 6 through the ignition device 16 are the same as those of the apparatus as shown in FIG. 12 for which description has been made with reference to FIGS. 5-8, and therefore, description of these structural elements is omitted.
In the conventional control apparatus having the construction described above, since the advance angle value is fixed when the ignition timing adjustment signal generator 3 is turned on, an in particular, since correction for stabilizing idling becomes null when idling operations are effected, control against the fluctuation of revolution number in the engine is lost. In particular, since the base fuel quantity calculated by the base fuel quantity operating means 12 is such as to provide a stoichiometric air-fuel ratio (A/F=14.7), it is not easy for the gas mixture to be stably burned. Therefore, fluctuation of the revolution number in the engine tends to be large. In a case that such period estimation type ignition timing control system is used, the estimation of the period becomes difficult when the fluctuation of the revolution number is large. When the actual ignition timing fluctuates, the adjustment of ignition timing becomes difficult.